Answer #5

drop TABLE if EXISTS track_downloads;

CREATE TABLE track_downloads  (
    download_id  SERIAL,
    track_id  INTEGER NOT NULL,
    user_id INTEGER NOT NULL,
    download_time timestamp without time zone NOT NULL
);

insert into track_downloads(track_id, user_id, download_time) VALUES
(1, 1, TO_TIMESTAMP('2010-11-19', 'YYYY-MM-DD')),
(1, 2, TO_TIMESTAMP('2010-11-19', 'YYYY-MM-DD')),
(2, 1, TO_TIMESTAMP('2010-11-19', 'YYYY-MM-DD')),
(2, 2, TO_TIMESTAMP('2010-11-19', 'YYYY-MM-DD')),
(2, 3, TO_TIMESTAMP('2010-11-19', 'YYYY-MM-DD')),
(1, 1, TO_TIMESTAMP('2010-11-18', 'YYYY-MM-DD')),
(1, 2, TO_TIMESTAMP('2010-11-18', 'YYYY-MM-DD')),
(2, 1, TO_TIMESTAMP('2010-11-20', 'YYYY-MM-DD')),
(2, 2, TO_TIMESTAMP('2010-11-20', 'YYYY-MM-DD')),
(2, 3, TO_TIMESTAMP('2010-11-20', 'YYYY-MM-DD'));

SELECT count(user_id), download_count from(
  select user_id, count(download_id) as download_count from track_downloads
  where download_time = '2010-11-19'
  group by user_id
) as t
group by download_count;